Negative forces on the lateral surface of metal pile foundations during sandy soil thawing

Introduction. Current Russian standards for the design of foundations on permafrost soils (SP 25.13330.2020) fail to sufficiently address the issue of accounting for negative forces during the thawing of the active layer when designing pile foundations in permafrost soils. As a result, designers face a choice either to account for negative forces, thereby increasing the reliability of the foundation design and its cost, or to neglect them, which reduces the cost of foundations but decreases their reliability. The present paper describes the results of studies on negative forces acting on the lateral surface of metal piles during seasonal thawing of permafrost soils represented by moderately saturated and fully saturated sands. Aim. To obtain a sufficient amount of experimental data for developing recommendations on accounting for negative friction forces acting on the lateral surface of pile foundations during the seasonal thawing of sandy soil. Materials and methods. The methodology involved conducting trough tests in a cooling chamber using pile models immersed in sand and suspended on crane scales. For tests, metal pipes of different lengths were immersed in sandy soils of medium and full water saturation. In addition, the study involved numeric thermotechnical calculations of the soil thawing rate and analytical calculations of the negative friction force based on SP 24.13330.2022 using reference values. Results. Proposals have been formulated to consider negative friction forces when designing pile foundations in thawing sandy soil. Conclusions. The analysis of experimental data revealed no negative forces on the lateral surface of piles during seasonal thawing of sandy soil.